Grumpy, the nut that was done up tight against the clutch half, according to advice I have received, is part of the locking system as you have intimated. Once undone the clutch half should (and I stress should) come off with the puller fairly easily.
But, using Murphy's Law, I agree with you, a trip to the local mechanic is the way to go, as it could be very well seized on the engine shaft and a bugger to get off...and the mechanic will have the tools and know-how to get it off successfully without damaging it, hopefully.
